Hi.

On Mon, Oct 26, 2020 at 04:13:26PM -0700, Roman Gushchin <g...@fb.com> wrote:
> Please note, that in the non-hierarchical mode all objcgs are always
> reparented to the root memory cgroup, even if the hierarchy has more
> than 1 level. This patch doesn't change it.
> 
> The patch also doesn't affect how the hierarchical mode is working,
> which is the only sane and truly supported mode now.
I agree with the patch and you can add
Reviewed-by: Michal Koutný <mkou...@suse.com>

However, it effectively switches any users of root.use_hierarchy=0 (if there
are any, watching the counters of root memcg) into root.use_hierarchy=1.
So I'd show them the warning even with a single level of cgroups, i.e.
add this hunk

@@ -5356,12 +5356,11 @@
                page_counter_init(&memcg->kmem, &root_mem_cgroup->kmem);
                page_counter_init(&memcg->tcpmem, &root_mem_cgroup->tcpmem);
                /*
-                * Deeper hierachy with use_hierarchy == false doesn't make
+                * Hierachy with use_hierarchy == false doesn't make
                 * much sense so let cgroup subsystem know about this
                 * unfortunate state in our controller.
                 */
-               if (parent != root_mem_cgroup)
-                       memory_cgrp_subsys.broken_hierarchy = true;
+               memory_cgrp_subsys.broken_hierarchy = true;
        }
 
        /* The following stuff does not apply to the root */

What do you think?

Michal

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